1. Technical Field
The present invention relates to a position sensor for a hydraulic actuator, and more particularly, to a position sensor capable of contactlessly detecting one or more operating positions of a hydraulic actuator utilizing the flow of working fluid and a hydraulic system using such a position sensor.
2. Related Art
A hydraulic system such as a machine tool is generally provided with hydraulic actuators that are operated under the control of a controller, so as to actuate various operating sections of the hydraulic system to thereby carry out desired operations. To this end, operating positions of the hydraulic actuators are detected by position sensors and supplied to the controller.
To detect the operating position of a hydraulic actuator, a limit switch serving as a position sensor is widely used. On the other hand, as a hydraulic actuator, a cylinder actuator is employed that has a cylinder body, a piston disposed to be movable therein, and a rod formed integrally with the piston and that is configured to move the rod back and forth by supplying and discharging working fluid to and from a cylinder chamber defined by the cylinder body and the piston.
The limit switch is provided with an operative element, i.e., a switch, disposed in the vicinity of a predetermined moving position of the rod. The operative element is actuated when a dog formed in the rod is brought in contact with the operative element during the rod movement, thereby detecting the operating position of the actuator.
In the case of position detection using limit switches, a hydraulic system requires a large number of limit switches each arranged to detect a corresponding one of objective operating positions of an associated cylinder actuator. This may cause difficulties in arranging some of the limit switches at their desired locations in narrow spaces around cylinder actuators associated therewith and in performing maintenance of these limit switches. Furthermore, a number of wires are required to connect the limit switches and the controller. Depending on circumstances in which limit switches are disposed, operative elements are sometimes exposed to the outside. This permits dusts and fluid drops to adhere to the operative elements, resulting in occurrences of operating failures and erroneous operations.
An object of the present invention is to provide a position sensor capable of contactlessly detecting one or more operating positions of a hydraulic actuator utilizing a flow of working fluid, without using a contact-type position sensor such as a limit switch.
Another object of the present invention is to provide a hydraulic system provided with the aforesaid non-contact type position sensor.
A position sensor according to the present invention comprises: at least one gear disposed in a fluid passage of a hydraulic actuator so as to be rotatable by a flow of working fluid in the fluid passage; a first sensing element, disposed to face the gear, for generating a first sensor output each time the gear rotates for a predetermined angle; a second sensing element, disposed to face the gear, for generating a second sensor output which is out of phase with the first sensor output each time the gear rotates for the predetermined angle; and a detecting section for determining an operating position of the hydraulic actuator based on the first and second sensor outputs supplied from the first and second sensing elements.
In the present invention, the gear of the position sensor rotates when working fluid flows in a fluid passage of a hydraulic actuator, and first and second sensor outputs that are out of phase with each other are supplied from the first and second sensing elements to the detecting section each time the gear rotates for a predetermined angle. From a phase relation between the first and second sensor outputs, the detecting section determines the direction of rotation of the gear indicative of the direction of the working fluid flow and, by extension, the direction of operation of the hydraulic actuator. Further, the detecting section can determine an amount of rotation of the gear indicative of an amount of operation of the hydraulic actuator based on the number of times for which the first or second sensor output is generated. Thus, an operating position of the hydraulic actuator can be determined based on the first and second sensor outputs.
As mentioned above, the position sensor of the present invention, having a sensing section comprised of a gear disposed in a fluid passage and two sensing elements disposed to face the gear, is capable of contactlessly detecting an operating position of a hydraulic actuator without using a contact-type sensing element such as a limit switch. In addition, the sensing section of the position sensor is not required to be disposed near the hydraulic actuator. Thus, it is easy to prevent dusts and fluid drops from adhering to the sensing section, thereby eliminating operating failures and erroneous operations of the sensing section. Also, a wire may be shortened in length that connects the sensing section with a detecting section of the position sensor. Furthermore, unlike a conventional position sensor having sensing sections such as limit switches that are provided for individual operating positions being detected, the position sensor of this invention can detect one or more operating positions of a hydraulic actuator by means of a single sensing section comprised of a gear and sensing elements. In other words, the sensing section of the position sensor of this invention serves as one or more limit switches. For this reason, it is enough to provide each position sensor with a single sensing section, even if two or more operating positions should be detected for each actuator. Accordingly, installation and maintenance of position sensors in a hydraulic system can be carried out with ease. The required number of wires connecting the sensing section of a position sensor with a detecting section thereof can be also reduced, and a frequency of occurrences of wire disconnection may be reduced.
In the present invention, preferably, each of the first and second sensing elements is comprised of a magnetic proximity sensing element disposed to face a peripheral portion of the gear, and the at least one gear is made of a metal material capable of influencing a magnetic field.
With this preferred arrangement, each sensing element supplies the sensor output to the detecting section each time a tooth portion of the gear passes in front of the sensing element, whereby the operating position of a hydraulic actuator can be contactlessly detected with reliability.
Preferably, the position sensor comprises first and second gears that are disposed in the fluid passage so as to be in mesh with each other and to be rotatable by a flow of the working fluid. More preferably, the first and second gears are disposed in the fluid passage so as to receive the flow of the working fluid at their portions where they are in mesh with each other.
According to this preferred arrangement, the flow of the working fluid acting on the first and second gears is converted into gear rotation with efficiency and accuracy, so that the first and second gears rotate in a manner appropriately following the flow of the working fluid, thereby improving the accuracy of detecting the operating position of the hydraulic actuator.
Preferably, the position sensor further comprises a sensor block that includes a sensor block body formed with first and second fluid passage portions constituting part of the fluid passage and having a first outer face to which respective one ends of the first and second fluid passage portions open, and a first plate attached to the first outer face of the sensor block body. The first plate is formed with a gear-accommodating space for receiving the at least one gear so as to be rotatable, the gear-accommodating space being communicated with the respective one ends of the first and second fluid passage portions.
With this preferred arrangement, the gear can be easily disposed in the fluid passage so as to be rotatable by a flow of working fluid by simply attaching the first plate that accommodates the gear to the sensor block body.
More preferably, the gear-accommodating space is formed so as to receive first and second gears to be in mesh with each other and to be rotatable by the flow of the working fluid. More preferably, the gear-accommodating space is formed so as to be communicated with respective one ends of the first and second fluid passage portions in vicinity of portions of the first and second gears where they are in mesh with each other.
According to these preferred arrangements, the flow of the working fluid is permitted to properly act on the gears.
Preferably, the position sensor further comprises a second plate attached to an outer face of the first plate on a side remote from the sensor block. The second plate is formed with an element-attaching section to which the first and second sensing elements are attached so as to face the gear.
With this preferred arrangement, the first and second sensing elements can be accurately disposed to face the gear by simply attaching the second plate, mounted with the sensing elements, to the first plate, whereby the position sensor can be simplified in construction and the detecting accuracy of the sensing elements can be improved.
A hydraulic system according to the present invention comprises: a working fluid source for supplying working fluid; one or more hydraulic actuators that are operable in response to supply of the working fluid; one or more fluid passages extending between the working fluid source and the one or more hydraulic actuators; one or more valves disposed in the one or more fluid passages for allowing or prohibiting the supply of the working fluid from the working fluid source to the one or more hydraulic actuators through the one or more hydraulic passages; a controller for drivingly controlling the one or more valves; and one or more position sensors disposed in the one or more fluid passages, each of the one or more position sensors being configured as mentioned in the above.
In the hydraulic system of the present invention, each of the one or more valves is drivingly controlled by the controller, to supply working fluid from the working fluid source through the associated fluid passage to a corresponding hydraulic actuator, thereby operating the same. At this time, the operating position of the hydraulic actuator is detected by the position sensor and is provided for control of the hydraulic actuator by means of the controller. The position sensor is configured as mentioned above, so that the aforementioned advantages can be attained such that the operating position of the hydraulic actuator can be contactlessly detected, to permit the controller to properly control the drive of one or more hydraulic actuators.
In the hydraulic system of the present invention, preferably, each of the one or more position sensors is disposed in the fluid passage between the valve and the hydraulic actuator, which individually correspond to the position sensor.
According to this preferred arrangement, the position sensor is disposed in a fluid passage region in which a flow of the working fluid is produced which adequately corresponds to the flow of the working fluid actually affecting on the operation of the hydraulic actuator, thus permitting the position sensor to accurately detect the operating position of the hydraulic actuator.
Preferably, each of the one or more valves is comprised of an electromagnetic changeover valve.
For instance, each electromagnetic changeover valve has first and second input ports and first and second output ports. The first and second input ports are connected to the working fluid source and a reservoir section for storing the working fluid therein. The first and second output ports are connected to first and second ports of a hydraulic actuator corresponding to the electromagnetic changeover valve, respectively. Under the control of the controller, the electromagnetic changeover valve assumes a first changeover position where the first and second input ports are individually communicated with the first and second output ports and a second changeover position where the first input port is communicated with the second output port and the second input port is communicated with the first output port. Alternatively, the electromagnetic changeover valve assumes the first or second changeover position or a neutral position where communication between the first and second input ports and the first and second output ports is prohibited.
With the aforesaid preferred arrangement using an electromagnetic changeover valve, the valve can be drivingly controlled by the controller with ease, with accuracy and with improved response.
More preferably, the hydraulic system has one or more position sensors each of which is configured as mentioned above. That is, each position sensor comprises a sensor block including a sensor block body formed with first and second fluid passage portions and having first outer face thereof to which respective one ends of the first and second fluid passage portions open, and each sensor block body has a second outer face thereof to which another end of the second fluid passage portion opens. The hydraulic system further comprises one or more valve blocks each attached to the second outer face of the sensor block body of a corresponding one of the one or more position sensors. Each valve block has a valve-attaching portion thereof to which a corresponding one valve is attached. The valve block is formed with a first fluid passage portion in alignment with another end of the second fluid passage portion formed in the sensor block body associated therewith.
More preferably, each sensor block body has a third outer face to which another end of the first fluid passage portion formed therein opens. Each sensor block body is further formed with third, fourth and fifth fluid passage portions having their opposite ends that open to the second and third outer faces of the sensor block body, respectively. Each valve block is formed with second, third and fourth fluid passage portions in alignment with respective one ends of the third, fourth and fifth fluid passage portions formed in the sensor block body associated therewith.
With the preferred arrangements, corresponding ones of the fluid passage portions formed in the valve block and the sensor block body can be communicated with one another by simply attaching the valve body, mounted with the valve, to the sensor block body. This facilitates the assembly of the hydraulic system and permits a simplified construction thereof.
More preferably, the hydraulic system further comprises one or more manifold blocks each attached to the third outer face of the sensor block body of a corresponding one of the one or more position sensors. Each manifold block is formed with first through fourth fluid passage portions in alignment with respective other ends of the first, third, fourth and fifth fluid passage portions formed in the sensor block body associated therewith.
This preferred arrangement makes it possible to simplify the fabrication and construction of the hydraulic system